Method of drying printed webs



Feb. 2l, 1961 H, C. EARLY TAL 2,972,196

METHOD 0F DRYING PRINTED WEBS Filed July 22, 1957 \\IIH/ y Q/ f/ L ////6 /NVENTO/P:

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United States Patent O METHOD OF DRYING PRINTED WEBS Harold C. Early and David B. Miller, Ann Arbor, Mich., assi'gnors to Meredith Publishing Company, Des Moines, Iowa, a corporation of Iowa Filed July 22, 1957, Ser. N0.\673,436

7 Claims. (Cl. 34-1) This invention relates to a method for drying printed webs. Modern web-fed rotary presses operate at web speeds in excess of 1000 feet per minute, and in some cases at speeds in excess of 1500 feet per minute. One of the problems in connection with the operation of high speed presses of this type involves the drying of the ink. At the present time the webs are passed through an oven in which hot air at about 600 F. is circulated over the web. In order to dry the ink thoroughly the web must remain in the oven for a comparatively long time, which greatly increases the size of the oven and the press assembly. Multicolor rotary ,presses are already enormous and require considerable plant space. Consequently, it is highly desirable to reduce as much as possible the space which is now utilized for drying the Webs. More seriously, however, at these drying temperatures the paper is substantially weakened due to exposure to heat. The paper reaches a temperature of about 300 F. Cellulose, when exposed to temperatures in this range, becomes considerably weakened and this frequently causes breakage of the web which, of course, is very aggravating as Well as expensive in shut-down time while the web is beingV mended.

Another serious disadvantage which results from heating the web at these elevated temperatures is the considerable shrinkage which occurs. The shrinkage results in uneven web tension which causes diliculty in obtaining intracolor register on the multicolor rotary presses. Furthermore, the dehydrated paper subsequently re-absorbs the moisture lost in drying. Where the printed sheets are formed into magazines which are securely stitched along one edge, the re-absorption of moisture from the air causes expansion, which results in wrinkled pages and difficulty in opening the magazine.

Another disadvantage in 'shrinkage is the waste of paper which necessarily results.

The primary object of this invention is to obviate these difficulties by drying the ink without heating more than the very surface of the web.

Another object Vis to provide a method vfor instantaneously ash drying the ink by moving the ink-coated web rapidly past an electrical heat source.

Another object is to provide a method of instantaneously drying all ink colors on a multicolored printed web.

In a preferred form of the invention an electric arc plasma (high temperature ionized gas) is brought into contact with the coated surface of the rapidly moving web. The intense heat of the plasma causes instantaneous evaporation of the solvent in the ink coating. The ash vaporized solvent is dissociated and ionized by the arc into monatomic molecules which recombine to form diatomic molecules at the paper surface with the evolution of large quantities of heat. Hence, the vaporized solvent actually participates as plasma in the drying operation. The dissociation takes place near the center of the arc while the recombination occurs toward the edge, nearer the surface of the paper. This method provides a very important advantage over prior art meth- '2,972,196` Patented Feb. 21, 1961 'ice ods of drying Webs. In conventional rvdrying with a gas flame or by means of hot air, the vaporized solvent driven from the surface of the paper forms an insulating vapor barrier over the surface. In accordance with the present invention this vapor barrier, which normally impedes drying, is utilized to accelerate drying.

It has also been recognized that swiftly moving webs carry an air film which acts as a thermal insulator. The electric arc method of the present invention causes this lm to be penetrated with little difficulty and is, theretfore, highly eective in drying high speed webs having the most tenacious air lilms associated therewith.

The arc plasma is produced by applying a high volt-V age of, say, v'1000 volts per inch of arc length across a pair of electrodes slightly Ispaced above the surface of the printed web. The arc may carry a current of from one to three amperes, preferably between one and two amperes. Hence, the power output may range from one to three kilowatts. 1f thecurrent is too high, there is a tendency lto scorch the web. The arc plasma is brought into contact with the Vsurface of the web by the force of a magnetic eld which conveniently may be supplied by an electromagnet disposed beneath the web opposite the arc. The strength of the magnetic eld may be in the order of several hundred gauss. The magnetic` intensity is not highly critical but, preferably, should not exceed about 1000 gauss. intensities in the range of 1000 gauss and over tend to cause the are plasma to as soon as it is formed. This lmay conveniently be .done

by passing a current of air over the arc, or by any other suitable means.

The electric arc referred to in this specification is not to heconfused with low current intermittent discharges such as corona discharges which are maesurable in tens or hundreds of milliamperes at voltages of -1000. The total power input per inch of discharge in such cases is a small fraction of the l to 3 kilowatts useful in the arcs of the present invention. This distinction is dscussed in some detail by William G. Dow in Fundamentals of Engineering Electronics, 2nd Edition, published by Iohn Willey & Sons, page 454. Electric arcs are well known in the art and are defined `by Cobine as follows: v

An arc at atmospheric pressure and above is characterized by a small intensely brilliant core surrounded by a cooler region of flaming gases, sometimes called the aureole. The aureole is a region of intense chemical activity, but the core is at such a high temperature that all gases are largely dissociated. If the arc occurs between highly refractory electrodes, such as carbon or tungsten, both the anode and the cathode are incandescent. (Gaseous Conductors by James Dillon Cobine, 1941, 2nd Edition published by Dover Publishing Inc. in 1958, page 290.)

Referring now to the drawing in which the single figure illustrates diagrammatically an apparatus suitable for carrying out the process of the invention, the web carrying the printed matter on the surface thereof is designated by the numeral 10. It is advancing at the rate of, say, 1200 feet per minute in the direction of the arrow. Tungsten electrodes 12 are provided, one on either side of the web just above the surface thereof. The electrodes may be made of carbon or other suitable material. The arc may be established conventionally by separation of the electrodes or by transition from a high voltage discharge. Voltage across the electrodes is of suticient magnitude' to provide approximatelyV r1000 volts per inch of 'arc length at a current of 4about two amperes. For a twelve-inch web therpotential would be 12,000 volts. The tungsten electrodes are mounted very close to the surface of the web but not in contact therewith. The intensity of the radiant energy is in the order of two kilowatts per square inch of web surface. For wide webs a s eries of staggered electrode pairs may be disposed across the Width of the web to avoid the necessity of employing extremely high voltages. The ink on the web traveling at 1200 feet per minute is dried within a few milliseconds by the bombardment of the surface with ions, electrons and molecules in the plasma. Intense heat is also produced by the recombination of monatomic molecules to diatomic molecules. Theintensity of the are will vary, ofcourse, with the speed of the web. Slower moving webs will require a lower voltage to prevent scorching. The amount of solvent in the ink also aects the drying rate.

Mounted beneath the electrodes and the web, coextensive therewith across the width of the web, is an electromagnet 14 for positioning the arc. The pole pieces 16 of the magnet terminate on either side of the electrodes. When power is applied to the electromagnet 14, the arc is pulled down into contact with the surface of the paper so that the column width is about to 1/2 inch. The fringing magnetic field positions the arc so that it can deviate only slightly from the desired position with a magnetic field intensity of about 300 gauss.

,Since the vaporized solvent from the arc is decomposed by the high temperature thereof, a comparatively cool ame is present around the arc column caused by burning constituents volatilized from the ink, including the solvent. In order to prevent carbon, which might be formedby burning these constituents in a deficiency of oxygen, from discoloring the paper, we have provided a hood 18 mounted directly over the electrode and extending across the width of the web. Disposed within the hood is an exhaust fan 20 which discharges volatilized materials to an exhaust duct 22. The hood also may serve as a reflector for the arc to intensify the radiation.

It will be appreciated that an apparatus of this kind requires little space as compared with a conventional long oven. In addition to saving space, the method of the invention reduces the cost of drying, and eliminates the problems resulting from shrinkage and broken webs. It effectively dries all colorsof ink in a multicolored print substantially instantaneously. Other modifications of the invention will occur to those skilled in the art. It is not our intention to limit the invention to the specific forms shown and described other than as necessitated by the scope of the appended claims.

-- Y2,972,196' Y' l l What we claim as new and desire to secure by Letters Patent of the United States is;

1. A method for drying ink on a printed web which comprises passing the web at a speed in excess of 1000 feet per minute immediately adjacent to a source of intense heat provided by an electric arc, while simultaneously subjecting the arc to a magnetic iield to bring the arc Vcolumn into contact with the surface of said moving web. Y

2. The method ofgclaim 1 which includes the additional step of exhausting the space around the arc to remove products volatilized from the ink.

3. A method for drying a web having'a coating thereon containing a volatile solvent which comprises passing the web immediately adjacent an electric arc while simultaneously subjecting the arc to a magnetic eld to bring the arc column into contact with the surface of the moving web, thereby evaporating the solvent and immediately transforming it intoan electrically conducting plasma to assist in heating the surface of the web.

4. The method of claim 1 wherein the power input to said arc is from 1 to 3 kilowatts per inch of arc length.

5. A method for drying ink on a printed web which' comprises passing the printed surface of the web at high velocity adjacent an electric arc While simultaneously subjecting the arc to a magnetic field of suicient intensity to hold the arc substantially stationary at said printed surface but not in excess of 1000 gauss.

6. The method of claim 5 wherein the power input to said arc ranges from about 1 to about 3 kilowatts per inch of arc length and the intensity of said magnetic field is about 300 gauss.

7. A method for drying ink on a printed web moving at high velocity which comprises contacting the surface of the web with an arc plasma formed by subjecting the ink, the surface of the web on which the ink is printed and the surrounding gas to an ultra-high-temperature electrical arc having a power output of one tothree kilowatts per inch of arc.

References Cited in the tile of this patent UNITED STATES PATENTS 1,503,224 Blaine July 29, 1924 1,557,730 Smith Oct. 20, 1925 1,646,010 Clover Oct. 18, 1927 2,042,145 Darrah May 26, 1936 2,266,392 Durant et al. Dec. 16, 1941 2,655,802 Ravich Oct. 20, 1953 2,674,050 Pound Apr. 6, 1954 FOREIGN PATENTS 25,117 Australia Oct. 23, 1936 OTHER REFERENCES A. P. Peck, Infra-Red Does the Trick, Scientific American, September 1941, pages 124-127.

Arum. 

